Field of the Invention
The present invention relates to a lens barrel used for optical apparatuses such as image capturing apparatuses and interchangeable lenses, and particularly to a lens barrel including a main aperture stop and a sub aperture stop.
Description of the Related Art
Lens barrels are each provided with an aperture stop for controlling a light amount from an object in order to achieve a proper exposure in image capturing.
In the aperture stop, a diameter of a light-passing aperture formed by multiple light-blocking blades (the diameter is hereinafter referred to as “an aperture diameter”) is set automatically depending on a photometry result or manually by a user. When the aperture diameter is changed depending on the photometry result, an actuator such as a stepping motor is used to drive the light-blocking blades in their opening/closing direction.
Furthermore, some lens barrels are each provided with, separately from a main aperture stop for mainly controlling the light amount as described above, a sub aperture stop for correcting a fully-opened aperture diameter in variation of magnification and focusing or for cutting flare. Such a sub aperture stop also can change its aperture diameter by moving multiple light-blocking blades in their opening/closing direction. However, providing actuators for the respective main and sub aperture stops hinders miniaturization of the lens barrel.
Japanese-Patent Laid-Open Nos. 2011-039107 and 06-018767 disclose lens barrels each including a mechanism for causing a main or sub aperture stop to perform opening/closing operations without using an actuator. In the lens barrel disclosed in Japanese-Patent Laid-Open No. 2011-039107, a driving arm, which extends obliquely to an optical axis direction (in which an optical axis extends) from a rotatable member provided to the sub aperture stop fixed in the optical axis direction, engages with an object side movable member. With a movement of the movable member in the optical axis direction, the rotatable member is rotated in a circumferential direction about the optical axis to change the aperture diameter of the sub aperture stop. In the lens barrel disclosed in Japanese-Patent Laid-Open No. 06-018767, an aperture stop (main aperture stop) is moved in the optical axis direction with variation of magnification and focusing, and a rotatable member (relaying member) provided to the aperture stop engages with an aperture interlocking member fixed in the optical axis direction in the variation of magnification and the focusing and has a sloped engaging face that engages with the aperture interlocking member. The rotatable member provided to the aperture stop is rotated in a circumferential direction about the optical axis in the variation of magnification and the focusing to change the aperture diameter of the aperture stop.
However, the lens barrel disclosed in Japanese-Patent Laid-Open No. 2011-039107 has a configuration that cannot change the aperture diameter of the sub aperture stop in only one of the variation of magnification and the focusing. Providing two sub aperture stops, one of which changes its aperture diameter in the variation of magnification and the other of which changes its aperture diameter in the focusing, separately from the main aperture stop may increase an entire length of the lens barrel or restrict an optical design freedom of the lens barrel. On the other hand, the lens barrel disclosed in Japanese-Patent Laid-Open No. 06-018767 includes the aperture stop whose aperture diameter is changed in the variation of magnification and the focusing. However, the aperture stop uses only one cam to change the aperture diameter, which makes it difficult to change the aperture diameter appropriately for combinations of various focal length and object distances.